x linked traits and chromosome theory of inheritance

Question 1

Chromosome theory of inheritance

Answer 1

Chromosome movements during meiosis parallel the behaviour of genes
two copies of each chromosome
pairs of homologous chromosomes segregate
non-homologous chromosomes assort independently

Question 2

chromosomes in humans

Answer 2

46 chromosomes
22 sets of autosomes
1 set of sex chromosomes (XX or XY)

Question 3

which gene on Y chromosome ensures testes develop

Answer 3

SRY gene

Question 4

what ensures equal numbers of males and females are produced

Answer 4

The segregation of sex chromosomes into gametes

Question 5

The single X chromosome in males must come from

Answer 5

the female

i think this means that transmission is from females

Question 6

x linked traits

Answer 6

1. Recessive X linked traits seen more frequently in males

= different phenotypic ratios for males and females

2. Reciprocal crosses give different results - breaks Mendels rules

Question 7

x linked trait e.g. fruit fly

3 points

Answer 7

1. eye colour
2. white eyes recessive
3. more common in males

Question 8

x linked trait e.g. colour blindness

Answer 8

1. x linked recessive

Question 9

Linked genes - genes close together on same chromosome

3 points

Answer 9

1. may be inherited together
2. their alleles are not assorted independently
3. dihybrid F2 ratios are not typical

Question 10

Linked genes - When genes are far apart on the same chromosome

Answer 10

crossing over may break the link

Question 11

Sex-limited traits

Answer 11

1. Traits only expressed by one sex
2. genes carried by both sexes
3. e.g. egg production (chickens)

Question 12

Sex-influenced traits

Answer 12

1. Expressed in both sexes but seen more frequently in one sex
2. horns in some sheep breeds

Question 13

Changes in chromosome number

2 points

Answer 13

1. disrupts development

2. influence of changes is more substantial than alterations in individual genes

Question 14

Aneuploidy

2 points

Answer 14

1. one or more extra / missing chromosomes
2. caused by nondisjunction

e.g. Trisomy 21
3 x chromosome 21
(cause of down syndrome)

Question 15

Polyploidy

3 points

Answer 15

1. three or more complete sets of chromosomes
2. normal condition in many plants
3. lethal condition in humans and many animals

Question 16

Changes in chromosome structure

four major types

Answer 16

1. deletions
2. duplications
3. inversions
4. translocations